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Single Idea 9544

[from 'An Introduction to Modal Logic' by GE Hughes/M Cresswell, in 5. Theory of Logic / K. Features of Logics / 4. Completeness ]

Full Idea

To say that an axiom system is 'weakly complete' is to say that every valid wff of the system is derivable as a thesis. ..The system is 'strongly complete' if it cannot have any more theses than it has without falling into inconsistency.

Gist of Idea

A system is 'weakly' complete if all wffs are derivable, and 'strongly' if theses are maximised

Source

GE Hughes/M Cresswell (An Introduction to Modal Logic [1968], Ch.1)

Book Reference

Hughes,G./Cresswell,M.: 'An Introduction to Modal Logic' [Methuen 1972], p.19


A Reaction

[They go on to say that Propositional Logic is strongly complete, but Modal Logic is not]